java.lang.NullPointerException: Attempt to invoke interface method 'java.util.Iterator java.util.List.iterator()' on a null object reference

I m currently working on a android apps which fetch data from parse server. I wanted to filter my recyclerView by using searchview. But it shows me nothing while search. It gives me error in this line*for (ParseObject parseObject : mRooms){ * Please help me to edit my code regarding this issues.

roomcardrecyclerviewadapter

private List<ParseObject> mRooms = new ArrayList<>();
private ArrayList<ParseObject> filterlist;
private ParseObject room;
private String mSection;
private Context context;
public RoomCardRecyclerViewAdapter(){
super(DIFF_CALLBACK);
}
public static final DiffUtil.ItemCallback<ParseObject>  DIFF_CALLBACK = new 
DiffUtil.ItemCallback<ParseObject>() {
@Override
public boolean areItemsTheSame(@NonNull ParseObject oldItem, @NonNull ParseObject newItem) {
return oldItem.getObjectId() == newItem.getObjectId();
}
@Override
public boolean areContentsTheSame(@NonNull ParseObject oldItem, @NonNull ParseObject newItem) {
return (oldItem.getUpdatedAt().equals(newItem.getUpdatedAt()) && 
oldItem.getCreatedAt().equals(newItem.getCreatedAt()));
}
};
public RoomCardRecyclerViewAdapter(String section) {
this();
this.mSection = section;
}
public RoomCardRecyclerViewAdapter(Context context, List<ParseObject>arrayList) {
this();
this.context = context;
mRooms = arrayList;
filterlist = (ArrayList<ParseObject>) arrayList;
}
public class RoomViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener{
protected ImageView mRoomImage;
protected TextView mRoomPrice;
protected TextView mInclusiveOrNot;
protected TextView mPropertyType;
protected TextView mNumOfBeds;
protected TextView mNumOfBaths;
protected TextView mRoomLocation;
private Context context;
public RoomViewHolder(Context context, View itemView) {
super(itemView);
mRoomImage = itemView.findViewById(R.id.room_image);
mRoomPrice = itemView.findViewById(R.id.price_label);
mInclusiveOrNot = itemView.findViewById(R.id.incl_excl_label);
mPropertyType = itemView.findViewById(R.id.propertyType_label);
mNumOfBeds = itemView.findViewById(R.id.num_beds_label);
mNumOfBaths = itemView.findViewById(R.id.details_num_baths_label);
mRoomLocation = itemView.findViewById(R.id.location_label);
this.context = context;
//set onclick listener
itemView.setOnClickListener(this);
}
@Override
public void onClick(View v) {
Log.i("Click event: ", "My room has been clicked.");
int pos = getAdapterPosition();
Intent intent;
ParseObject room = getCurrentList().get(pos);
//create the ParseObject proxy
ParseProxyObject roomProxy = new ParseProxyObject(room);
Toast.makeText(context, room.getString("roomSuburb"), Toast.LENGTH_LONG).show();
//fork to corresponding activity
if(mSection != null) {
Log.i("mSection text: ", "mSection text is: " + mSection);
if (mSection.equals("My Rooms")) {
//start my rooms detail activity
Log.i("My room: ", "Room selected " + roomProxy.getObjectId());
intent = new Intent(context, MyRoomDetailActivity.class);
//add the room to the intent
intent.putExtra("currentSelectedRoomObject", room);
Log.i("Selected room", "Put Extra, " + room);
intent.putExtra("roomObject", roomProxy);
context.startActivity(intent);
}
}else {
Log.i("My room:", "RoomDetailActivity loaded for MyRoomDetail Activity instead");
intent = new Intent(context, RoomDetailActivity.class);
//add the proxy to the intent
intent.putExtra("roomObject", roomProxy);
context.startActivity(intent);
}
}
}
@Override
public RoomViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
//inflating the viewholder with the appropriate views
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.room_cardview, parent, 
false);
return new RoomViewHolder(parent.getContext(), view);
}
@Override
public void onBindViewHolder(@NonNull RoomViewHolder holder, int position) {
room = getItem(position);
holder.mRoomLocation.setText(room.getString("roomSuburb"));
holder.mRoomPrice.setText(Integer.toString(room.getInt("roomMonthlyRent")));
holder.mInclusiveOrNot.setText(room.getString("roomRentInclusiveOfBills"));
holder.mPropertyType.setText(room.getString("roomPropertyType"));
holder.mNumOfBeds.setText(Integer.toString(room.getInt("roomBedrooms")));
holder.mNumOfBaths.setText(Integer.toString(room.getInt("roomBathrooms")));
@Override
public Filter getFilter(){
return new Filter() {
@Override
protected FilterResults performFiltering(CharSequence charSequence) {
String charString = charSequence.toString();
if (charString.isEmpty()){
room = (ParseObject) mRooms;
}else {
List<ParseObject> filteredList = new ArrayList<>();
for (ParseObject parseObject : mRooms){
if (parseObject.getString("roomSuburb").toLowerCase().contains(charString.toLowerCase())){
filteredList.add(parseObject);
}
}
room = (ParseObject) filteredList;
}
FilterResults filterResults = new FilterResults();
filterResults.values = room;
return filterResults;
}
@Override
protected void publishResults(CharSequence charSequence, FilterResults filterResults) {
room = (ParseObject) filterResults.values;
notifyDataSetChanged();
}
};
}

mainActivity

mHomeSectionsPagerAdapter = new 
HomeSectionsPagerAdapter(getSupportFragmentManager());
roomCardRecyclerViewAdapter = new RoomCardRecyclerViewAdapter(this, 
mRooms);
mRooms = new ArrayList<>();
// Set up the ViewPager with the sections adapter.
mViewPager = findViewById(R.id.container);
mViewPager.setAdapter(mHomeSectionsPagerAdapter);
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
final ParseQuery<ParseUser> query = ParseUser.getQuery();
//get the search view and set the searchable configuration
SearchManager searchManager = (SearchManager) 
getSystemService(Context.SEARCH_SERVICE);
MenuItem item = menu.findItem(R.id.search);
SearchView searchView = (SearchView) MenuItemCompat.getActionView(item);
//assumes the current activity is the searchable activity
searchView.setSearchableInfo(searchManager.getSearchableInfo
(getComponentName());
searchView.setSubmitButtonEnabled(true);
searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
@Override
public boolean onQueryTextSubmit(String query) {
roomCardRecyclerViewAdapter.getFilter().filter(query);
return false;
}
@Override
public boolean onQueryTextChange(String newText) {
roomCardRecyclerViewAdapter.getFilter().filter(newText);
return false;
}
});
return true;
}
@Override
public boolean onSearchRequested() {
//pauseSomeStuff();
//roomCardRecyclerViewAdapter.getFilter().filter(query);
return super.onSearchRequested();
}

I think problem is here:

You haven't shared first lines of MainActivity where you declare your variables. So, I assume that you have some code like this:

List mRooms;

Then I assume that, before assigning value to this mRooms you have passed it to RoomCardRecyclerViewAdapter:

roomCardRecyclerViewAdapter = new RoomCardRecyclerViewAdapter(this, mRooms);
mRooms = new ArrayList<>();

Then you have assigned value to mRooms. That's why you get NPE. You can solve this problem just like this:

mRooms = new ArrayList<>();
roomCardRecyclerViewAdapter = new RoomCardRecyclerViewAdapter(this, mRooms);